1. Field of the Invention
The present invention relates to a process for making light-colored petroleum resins from fractions of distillates derived from petroleum cuts that have undergone steam cracking, as well as resins displaying the above characteristics.
More particularly, this invention relates to hydrocarbon resin hydrogenations by a heterogeneous catalyst where high molecular weights lead to diffusion limitations as in the hydrogenation and decolorization of a hydrocarbon resin prepared by the thermal polymerization of cyclopentadiene and methylcyclopentadiene in the liquid phase or mixed phase.
2. Description of the Prior Art
It is known that from steam cracked petroleum distillate fractions, having boiling points within the range 20.degree./280.degree. C., it is possible to prepare resins of medium to high softening point by thermal polymerization carried out at a temperature of, for preference between 160.degree. and 320.degree. C., at a pressure for preference between 10 and 30 atmospheres; the polymer obtained is distilled at a temperature between 220.degree. and 350.degree. C., with or without the injection of superheated steam.
Although the resins thus obtained have some interesting properties, they have the disadvantage of a rather dark color. These resins have the further disadvantage that they are thermally and oxidatively unstable, i.e., they are chemically reactive.
In United Kingdom Specification No. 1,202,802, the inventors teach that it is possible to obtain resins with a high softening point and pale color, by subjecting a resin obtained by thermal polymerization from steam cracked petroleum distillate fractions, preferably having a boiling point between 20.degree. and 280.degree. C., to catalytic hydrogenation, said fractions usually of compounds having one or more unsaturated cyclic rings in the molecule, such as cyclodienes, cycloalkenes, and indenes.
Suitable hydrogenation catalysts include nickel, reduced nickel, molybdenum sulphide, with a preferred catalyst being a pre-activated catalyst on a kieselguhr support containing about 58% by weight of nickel, the specific area being about 140 m.sup.2 /g and the ratio: reduced nickel to total nickel equal to about 0.66. Suitable proportions total nickel of catalyst are from 5 to 20% by weight, and for preference from 7 to 13% by weight, in relation to the resin.
Before carrying out hydrogenation, the thermally polymerized resin is preferably dissolved in a saturated hydrocarbon solvent such as heptane. Hydrogenation can take place in a single stage at a temperature of 200.degree. to 260.degree. C. and for preference from 210.degree. to 230.degree. C., at a pressure of 20 to 120 atmospheres, and for preference from 30 to 90 atmospheres for a period of 5 to 7 hours. After filtering off the catalyst, the solvent is removed by distillation and recovered for recycling.
In this way is obtained, with a yield generally in the order of 90-95% (in relation to the thermal resin treated), a hydrogenated resin characterized by a Gardner color in the region of 1 to 3, a softening point in the region of 150.degree. to 180.degree. C., and a bromine number in the region of 1 to 3.
In the production of these resins, the amount produced is limited particularly by the feed throughput and catalyst lifetime.
Accordingly, in view of the above, the need has existed for an improved process providing for increased yield of hydrocarbon resins of quality comparable or superior to that produced by the prior art processes and in addition, operating with catalysts and process conditions resulting in longer run lengths.